There's a reason "The Night Before Christmas" states "Not a creature was stirring, not even a mouse." This is a holiday story. Anyone that has watched mice knows that they move constantly. They twitch their nose and turn their body left and right and fidget forward, dragging their tails in a search for food. That is, until they have trouble finding morsels. Then the brain releases a hormone called FGF21, which causes a lowered metabolism and a state of "hibernation", according to a study released June 5 in Cell Metabolism. The hormone tells the mouse to burn it's own fat instead of acquired carbohydrates. Its body temperature and metabolism decrease as a result--to promote survival. Less calories are burned and so less are needed. Scientists hope to harness this hormone and turn it into a drug to treat obese people. That way, at least they won't be stirring under midnight temptations to steal Santa's cookies. But I'm sure the same desire won't be curbed in mice.